Interpretive Summary: The ambrosia beetles Xylosandrus germanus and Xylosandrus crassiusculus are serious pests in ornamental tree nurseries. Xylosandrus germanus and X. crassiusculus spend the winter as adults in infested trees. They emerge in spring and fly into nurseries to colonize new trees. Nursery growers rely on trunk sprays of insecticides to protect their trees (prevent colonization) from these beetles. However, these beetles are very small and difficult to detect so it’s difficult for growers to synchronize their sprays with beetle activity. If sprays are applied too late damage has already occurred, if they are applied too early more sprays are applied than necessary. The current research developed tools to detect and forecast spring activity of Xylosandrus species, enabling growers to better synchronize their sprays with beetle activity. Ethanol-baited traps were shown to be reliable tools for monitoring initial activity of X. germanus and X. crassiusculus in nurseries. The bloom sequence of woody ornamental plants was also a good predictor of initial spring X. germanus activity in Ohio. These tools can be used by growers to time their first sprays in spring. After X. germanus started emerging in spring, temperature was a good predictor of activity. No X. germanus flight or attack activity occurred unless temperatures were at least 68 degrees F. Growers can use this information to decide when to apply sprays. If the extended weather forecast predicts cool weather (temperatures below 68F), growers can wait for warmer weather to apply sprays. This should help growers reduce the number of sprays they use, which will save them money and reduce environmental impact of pest control.

Technical Abstract:
Wood-boring ambrosia beetles (Coleoptera: Curculionidae: Scolytinae), including Xylosandrus spp., are key pests in ornamental nurseries. Knowledge of their activity in spring is important for nursery growers to effectively time their protective sprays. We evaluated the reliability of ethanol-baited bottle-traps for monitoring emergence of overwintered Xylosandrus spp. in ornamental nurseries. Detection of initial flight activity by traps was compared with initial attacks on ethanol-injected trap-trees. To develop tools for forecasting X. germanus activity, the relationships between temperature and the attack and flight activity were examined, and the bloom sequence of ornamental plants was examined as phenological indicators of X. germanus emergence in Ohio. Captures of Xylosandrus germanus (Blandford) coincided with attacks on trap-trees on seven of eight occasions over two years in four nurseries. There was a strong relationship between maximum daily temperatures 20°C and 21°C and X. germanus attack and flight activity. No attack or flight activity were detected in a monitoring period unless there was one or two days, respectively, above 20°C. Emergence of X. germanus always began after and within 6 days of full bloom on Cornelian cherry dogwood, and usually after and within 4 days of first bloom on Norway maple and full bloom on border forsythia. The traps or phenological indicators can be used by growers to monitor emergence of X. germanus to time their initial protective sprays. The relationship between X. germanus activity and temperature can be used by growers to make decisions on timing subsequent treatments.